Genome-wide identification of expansin in Fragaria vesca and expression profiling analysis of the FvEXPs in different fruit development

Genome-Wide Identification of Expansins in Rubus chingii and Profiling Analysis during Fruit Ripening and Softening

Improving fruit size or weight, firmness, and shelf life is a major target for horticultural crop breeding. It is associated with the depolymerization and rearrangement of cell components, including pectin, hemicellulose, cellulose, and other structural (glyco)proteins. Expansins are structural proteins to loosen plant cell wall polysaccharides in a pH-dependent manner and play pivotal roles in the process of fruit development, ripening, and softening. Rubus chingii Hu, a unique Chinese red raspberry, is a prestigious pharmaceutical and nutraceutical dual-function food with great economic value. Thirty-three RchEXPs were predicted by genome-wide identification in this study, containing twenty-seven α-expansins (EXPAs), three β-expansins (EXPBs), one expansin-like A (EXPLA), and two expansin-like B (EXPLBs). Subsequently, molecular characteristics, gene structure and motif compositions, phylogenetic relationships, chromosomal location, collinearity, and regulatory elements were further profiled. Furthermore, transcriptome sequencing (RNA-seq) and real-time quantitative PCR assays of fruits from different developmental stages and lineages showed that the group of RchEXPA5, RchEXPA7, and RchEXPA15 were synergistically involved in fruit expanding and ripening, while another group of RchEXPA6 and RchEXPA26 might be essential for fruit ripening and softening. They were regulated by both abscisic acid and ethylene and were collinear with phylogenetic relationships in the same group. Our new findings laid the molecular foundation for improving the fruit texture and shelf life of R. chingii medicinal and edible fruit.

Evolution and Expression of the Expansin Genes in Emmer Wheat

Expansin proteins, a crucial class of intracellular proteins, are known to play a vital role in facilitating processes like cell wall relaxation and cell growth. Recent discoveries have revealed that expansin proteins also have significant functions in plant growth, development, and response to resistance. However, the expansin gene family, particularly in emmer wheat, has not been thoroughly studied, particularly in terms of evolution. In this study, we identified 63 TdEXPs and 49 TtEXPs from the latest genome versions of wild emmer wheat (WEW) and durum wheat (DW), respectively. The physicochemical properties of the encoded expansin proteins exhibited minimal differences, and the gene structures remained relatively conserved. Phylogenetic analysis categorized the proteins into three subfamilies, namely EXPA, EXPB, and EXLA, in addition to the EXLB subfamily. Furthermore, codon preference analysis revealed an increased usage frequency of the nucleotide "T" in expansin proteins throughout the evolution of WEW and DW. Collinearity analysis demonstrated higher orthology between the expansin proteins of WEW and DW, with a Ka/Ks ratio ranging from 0.4173 to 0.9494, indicating purifying selection during the evolution from WEW to DW. Haplotype analysis of the expansin gene family identified five genes in which certain haplotypes gradually became dominant over the course of evolution, enabling adaptation for survival and improvement. Expression pattern analysis indicated tissue-specific expression of expansin genes in emmer wheat, and some of these genes were quantified through qRT-PCR to assess their response to salt stress. These comprehensive findings present the first systematic analysis of the expansin protein gene family during the evolution from WEW to DW, providing a foundation for further understanding the functions and biological roles of expansin protein genes in emmer wheat.

Pathotypes of Fusarium oxysporum f. sp. fragariae express discrete repertoires of accessory genes and induce distinct host transcriptional responses during root infection

Convergent evolution of phytopathogenicity is poorly described, especially among multiple strains of a single microbial species. We investigated this phenomenon with genetically diverse isolates of Fusarium oxysporum f. sp. fragariae (Fof) that cause one of two syndromes: chlorosis and wilting (the 'yellows-fragariae' pathotype), or only wilting (the 'wilt-fragariae' pathotype). We challenged strawberry (Fragaria × ananassa) plants to root infection by five fungal isolates: three yellows-fragariae, one wilt-fragariae and one that is not pathogenic to strawberry. All Fof isolates had chromosome-level assemblies; three were newly generated. The two pathotypes triggered distinct host responses, especially among phytohormone-associated genes; yellows-fragariae isolates strongly induced jasmonic acid-associated genes, whereas the wilt-fragariae isolate primarily induced ethylene biosynthesis and signalling. The differentially expressed genes on fungal accessory chromosomes were almost entirely distinct between pathotypes. We identified an ~150 kbp 'pathogenicity island' that was horizontally transferred between wilt-fragariae strains. This predicted pathogenicity island was enriched with differentially expressed genes whose predicted functions were related to plant infection, and only one of these genes was also upregulated in planta by yellows-fragariae isolates. These results support the conclusion that wilt- and yellows-fragariae cause physiologically distinct syndromes by the expression of discrete repertoires of genes on accessory chromosomes.